FP_ZERO

From Cppreference

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Defined in header <cmath>
#define FP_ZERO /*implementation defined*/		(C++11 feature)

The FP_ZERO macro expands to an integer constant expression. It represents a type of floating point values and indicates that the value is positive or negative zero.

[edit] See also

fpclassify (C++11)	categorizes the given floating point value (function)
FP_INFINITE (C++11)	indicates infinite floating point value (macro constant)
FP_NAN (C++11)	indicates not-a-number (NaN) (macro constant)
FP_NORMAL (C++11)	indicates normal number (macro constant)
FP_SUBNORMAL (C++11)	indicates subnormal number (macro constant)